DESCRIPTION (Adapted from applicant's description): The overall goal of these studies is to test the hypothesis that there is an interaction between increased secretion of adrenal corticosteroids and increased secretion of estrogen during pregnancy which is necessary for normal blood pressure control in the peripartal period. Studies in pregnant, hypocorticoid ewes and clinical experience in pregnant women with hypoadrenocorticism suggest that normal blood pressure control in late pregnancy requires increased adrenal secretion. Insufficient supply of cortisol results in rapid and profound hypotension, with increased morbidity and mortality in both mother and fetus. The experiments in this proposal will directly test the hypothesis that a decrease in cortisol at a time of increased estrogen results in a greater decrease in vascular reactivity to phenylephrine and that this correlates with increased production of nitric oxide production in one or more sites in the body. Four groups of ewes will be studied: adrenalectomized, ovariectomized ewes, adrenalectomized ovariectomized ewes treated with estradiol, adrenal- intact ovariectomized ewes, and adrenal-intact ovariectomized ewes treated with estradiol. All adrenalectomized ewes will be treated with aldosterone and cortisol for one week following surgery, and then the adrenal steroid infusions will be stopped to produce the hypoadrenal state. Animals will be studied at a time point (8 hours) in which the adrenalectomized estrogen treated animals are hypotensive, but the adrenalectomized ewes without estradiol treatment are not overtly hypotensive. Experiments will test vascular reactivity in response to phenylephrine in all 4 groups of ewes to test the hypothesis that estrogen administration decreases vascular reactivity in adrenalectomized ewes. Experiments will also determine plasma levels of nitrates and nitrites and the ability of infusion of L-NAME, an inhibitor of nitric oxide synthase (NOS), to increase vascular reactivity in adrenalectomized ewes with estradiol treatment. Experiments will also test the concentrations of cGMP, and levels of iNOS, eNOS, and nNOS protein measured by Western analysis and mRNA by RT-PCR in aorta, uterine artery, mesenteric artery, renal artery, renal interlobular artery, renal medulla and cortex, and skeletal muscle, taken from animals in the same 4 experimental groups. These experiments will determine if absence of cortisol results in increased NOS in one or more of these sites. Samples of tissue will also be examined by immunohistochemistry to more precisely identify the cell populations containing iNOS, eNOS or nNOS in these ewes. These experiments will therefore describe which isoform(s), and in which cells, NOS is altered by cortisol withdrawal, either alone or in combination with increased estrogen. This information will form the basis of future experiments to determine the mechanism of the interaction of estrogen and cortisol in control of NO and regulation of blood pressure during pregnancy. These studies will therefore add to our understanding of normal blood pressure control during pregnancy, and of the pathophysiology of hypoadrenocorticism at term. These studies will also to our understanding of the counterbalancing effects of increased cortisol and increased estrogens in control of normal blood pressure in normal pregnancy.